Title page for ETD etd-12122006-160217

Trees and Structural Soil as a Stormwater Management System in Urban Settings

Degree

Master of Science

Department

Horticulture

Advisory Committee

Advisor Name

Title

Day, Susan D.

Committee Co-Chair

Harris, James Roger

Committee Co-Chair

Dove, Joseph E.

Committee Member

Wynn, Theresa M.

Committee Member

Keywords

compacted soils

Acer rubrum

submerged soils

tree roots

water body pollution

infiltration rate

Quercus velutina

urban forestry

urban runoff

street trees

Fraxinus pennsylvanica

Quercus bicolor

Date of Defense

2006-12-05

Availability

unrestricted

Abstract

Urban runoff continues to impair water quality and there is an increasing need for stormwater management within the limited confines of urban spaces. We propose a system of structural soil and trees that can be incorporated beneath pavement. Structural soil has a high load-bearing capacity yet is engineered to support tree root growth. Stormwater is directed into a structural soil reservoir below the pavement where tree roots can also thrive.

Two container experiments evaluated tree function in this system. We examined whether tree roots can grow into compacted subsoils and if root penetration increases soil infiltration rate. Quercus velutina, Acer rubrum, and a no-tree variant were planted in 26.5 L (7 gal) containers and the rootballs surrounded by compacted clay loam. Roots grew into all layers of the compacted soil. Infiltration rate increased by 63% (+/-2%) compared to no-tree containers. A second experiment evaluated water uptake and tree development in fluctuating water tables. Quercus bicolor and Fraxinus pennsylvanica were planted in 94.6 L (25 gal) containers with structural soils (either Stalite or CU® Structural Soil). Trees were subjected to fluctuating water tables simulating infiltration rates of 2, 1, and 0.1 cm/hr for two growing seasons.

Trees thrived in all infiltration regimes but roots were shallower in slowly drained treatments. Trees grew best and transpired the highest water volume with moderate infiltration. Even if trees uptake only small volumes of water, increased canopy size compared to conventional plantings (because of greater penetrable soil volume) allows greater rainfall interception thus decreasing runoff.